Electron discharge device



3 1935. H. w. PARKER 2,006,716

ELECTRON DI SCHARGE DEVI CE Filed Dec. 27, 193.0

INVENTOR fi nry W PUP/r61".

ATTORNEY Patented July 2, 1935 I aooana, I ELECTRON DISCHARGE DEViCE Henry W. Parker, Toronto, Ontario, Canada,.as-

signpr to Rogers-Radio Tubes, Limited, Toronto, Ontario, Canada, a. corporation .of Ontario,

Canada swim-men December 27,1930. Serial No. 505,045 f 3 Claims. 01. gee-27.5)

My invention pertains in general to electron discharge devices of the type known as thermionic tubes which employ a screening grid in addition to the control grid. I

The function of the screen grid in athermionictube as is well known is, briefly, to improve conductance and hence the effie-iency' of the-tube through-eliminating as nearly as possible electrostalticcoupling-between the control grid and the anode of the tube and space charge eifect between the cathode and anode. The screen grid, to function efiiciently as an electrostatic shield, must be composed of many turns of'wire disposed with a relatively small space between adjacent turns, or of a screen having a fine mesh. Such construction, however, produces an undesirable effect in that the projected area of such a grid with respect to the anode is relatively large and hence the screen intercepts a considerable portion of the electrons flowing to the anode to, in effect, reduce the gain achieved by the electrostatic screening. The ideal screen, of course, would be one which, while functioning to eliminate the space charge effect, offered no impediment whatever to the flow of electrons between the cathode and the anode.

An object of my invention is toprovide a screen grid for thermionic tubes which in a great degree approaches the above noted characteristics of an ideal screen.

Another object of my invention comprises producing a screen grid whereby the desired electrostatic screening effect may be obtained with minimum interception of the electron stream.

A still further object of my invention comprises producing a screen grid whereby the conductance of the tube is increased to thus increase the overall efficiency of the tube.

I accomplish all of the above noted desirable features by providing a screen grid in the form of two or more grids, each having a relatively coarse mesh and all electrically connected to a common terminal.

In the figures accompanying and forming a part of this specification and in which like reference numerals designate corresponding parts throughout:

Fig. 1 is a partially sectioned elevation of a thermionic tube provided with my improved screen grid and with the enclosing envelope omitted.

Fig. 2 is a sectional plan view of the same take on the line 22 of Fig. 1.

Referring now particularly to the figures which illustrate one form of screen grid tube incorporating m novel screen grid. The ress i sup orts the usual anode iieoneentric'ally located within which'i's the cathode ii which I have arbitrarily chosen toilliistrate as or the indirect heated employing a heating wire Surrounding the cathode 2 there is provided the usual control grid 4, supported by sta'fdards 9 and I8, and pro'-' vided with the usual terminal it. 1

My 1 improved screen grid comprises-two grids of relatively coarse mesh as shown, concentrically disposed with respect to each other and maintained between the control grid 4 and the anode i2 as illustrated. The screen grid I have v chosen to illustrate comprises two helices of wire which are spot-welded or otherwise attached to supports as 5 and t3 and these supports are shown connected together, thus electrically connecting the two grids, by conductors Ii. The grids thus united are supported in the press by the *standards l and 8 one of which 1, serves as a terminal therefor and are maintained in relative position with respect to the other elements of the tube by the perforated mica disk l5 which is supported by the cathode 2.

It will be noted that the mesh of these two screen grids is considerably coarser than that of the control grid and that they therefore produce a relatively smaller projected area on the anode and hence intercept only a small portion of the electron stream passing from the cathode to the anode. The two grids taken jointly thus present a smaller obstruction to the electron space current flow to the anode than would be caused by a single grid having a much closer mesh and consequently the same electrostaticl screening capacity. so far as the amplification constant of the tube is concerned, one of multiplication. For instance, if a single grid is closely wound to give an amplification constant of 54, then a double grid with much wider spacing between the turns, each having a Mu of 8, will give the same amplification constant because the product of the Mu of one screen by that of the other is equal to 3 x 8, or 64. In other words, While a single screen of coarse mesh would produce an-ampli fication lower than that desired, a plurality of such screens serves to multiply the amplification The effect of one grid upon another is, I

struction to the electron flow, I am able to prostructed, I have been able, through the use of my improved screen grid, to build tubes in which the screen intercepts only about one-third of the electron stream intercepted .by screens now com- 'mon in the art, to increase in a marked manner the anode conductance, while maintaining 'the "desired degree of electrostatic'screening and high amplification constant.

While I have chosen to illustrate my improved screen grid as used in conjunction with a thermionic tube utilizing only an inner screen instead of both an innerand outer screen, itis of course obvious that my screen grid will function with both types of construction equally well.

liaving thus completely described and disclosed my invention, what I claim as'new and desire to secure by- Letters Patent oi the United St 5 a -followsr .1. p

1. In an electron discharge device, a sealed container, a cathode, an anode, and a control electrode within said container, and an electrostatic screen composed of a plurality ofseparate screening members each including a conductor disposed in the form of a helix, the open area of which is considerably greater than the-solid area thereof, completely surrounding said. cathode,

said members being electrically interconnected and positioned onewithin the other between said control electrode and said anode. r v

2. In an electron, discharge device, a sealed containena' cathode, an anode, andamesh control electrode within said container, and an electrostatic screen composed of a plurality of screens of relatively coarser mesh than that of said control electrode, each encircling said cathode, conelectrically interconnected and maintained between said control electrode and said anode,

3. In' an electron discharge device, a sealed container, a plurality of electrodes including a cathode, an anode, and a control electrode with- 'insaid container, and an electrostatic screen 'centrically disposedwith respect to each other, 1

composed of ,a plurality of separate screening members each including a conductor disposed in a the form of a helix, the open area 01 which is-considerably greater than the solid area thereof, S111:- rounding said cathode, id members beingelectrically connected and positioned one-within the other between said control electrode, and said anode. 1 I r H HENRY W. PARKER. 

